This invention relates to coating apparatus wherein a solid applicator contacts the work, with a cleaner for the applicator. More particularly, this invention relates to a glue applicator of the type used to apply liquid glue to sheet material, such as to blanks which are ultimately formed into paper boxes.
Prior art glue applicator equipment has been developed for the purpose of feeding sheets of material in sequence to a series of processing stations and coating the sheets of material with glue and other liquids at one or more of the processing stations. These machines typically include equipment for picking off the end sheet from a stack of material, feeding the sheet along a path generally parallel to the plane of the sheet material into contact with the cylindrical surface of a rotating cylindrical glue applicator roll, picking the sheet off the glue applicator roll and passing the sheet to various subsequent work stations. The glue applicator roll continuously rotates in contact with a glue wetting roll which is partially submerged in a body of liquid glue or other liquid. The liquid is transferred from the body of liquid glue by the wetting roll to the applicator roll, and then to the sheet material. As a system operates, the liquid glue tends to accumulate and to harden on the various parts of the processing equipment, particularly on the end portions of the glue wetting roll. The accumulation of glue at the ends of the glue wetting roll is undesirable, particularly because an accumulation of glue tends to interfere with the proper continuous operation of the equipment.
Various wiper blades and other devices have been used in the past to scrape or wipe glue from the ends of cylindrical rolls. For example, my previous U.S. Pat. No. 4,119,057 illustrates a wiper for wiping the end surfaces of a glue applicator roll. Since the glue wetting roll is partially submerged in the liquid glue in the glue pan, the ends of the glue wetting roll become coated with glue, and a large amount of glue must be wiped or otherwise removed from the ends of the wetting roll. If the glue is allowed to accumulate without removal on the ends of the wetting roll, the build-up of glue eventually obstructs the operation of the equipment. Moreover, when the glue is wiped from the ends of the glue wetting roll, it is important that all of the glue be wiped from the end of the roll, without leaving any annular bands of glue passing between the wiper and the end surface of the wetting roll. If such annular bands of glue are permitted to remain on the ends of the wetting roll, these bands eventually become hard, they increase in size, and they tend to cut into the material of the wiper, thus tending to destroy the wiper.
When the glue is transferred from the wetting roll to the glue applicator roll, substantially the entire surface of the glue applicator roll is coated with glue. When the sheet material moves into contact with the glue applicator roll, usually the sheet material is of less width than the length of the glue applicator roll, and therefore contacts only the central portion of the glue applicator roll. After the sheet material contacts the glue applicator roll it tends to cling to the applicator roll until it is picked off the applicator roll by picks, whereupon the sheet material is diverted toward a subsequent processing station. The picks must be positioned in sliding contact with the glue applicator roll, usually in the middle portion of the glue applicator roll so as to make contact with the sheet material. Thus, as the machine operates, the glue applicator roll eventually becomes worn more in its central portion than at its end portions, causing a slight reduction in diameter about its central portion. The reduced diameter at the central portion of the applicator roll causes the roll to apply an uneven coating of glue on the sheet material. Thus, it is important that the glue applicator roll be fabricated from material that does not deteriorate rapidly from the continuous contact by the pickers and sheet material.